We propose to continue our studies towards developing a non-invasive probe of lipid configuration and bilayer fluidity in biological membranes with specific emphasis on photo-receptor membrane. To this end we will primarily use the relatively new techniques of Raman spectroscopy and Fourier Transform Infrared Spectroscopy to measure the vibrational spectra of photoreceptor membrane lipids as a function of temperature and environment. Our studies will also include model systems where appropriate. We have recently shown that by utilizing selectively deuterated lipids one can obtain detailed information regarding the variation of lipid fluidity at different locations in the membrane in both the gel and liquid crystal phases. We propose to use this model system to investigate the perturbing effects of membrane active antibiotics on the fluidity of the bilayer. We will also utilize recently developed delipidation and reconstitution methods to obtain the vibrational spectra of photoreceptor membrane protein and lipid. In addition to studies with photoreceptor membranes we will also examine purple membrane from Halobacterium Halobium as an important model system for studies of visual mechanisms.